This invention relates to scavenger systems utilized to remove waste gases including anesthetic gases from areas where such gases are susceptible of inhalation by personnel.
There are, of course, many different types of machines adapted to provide an anesthetic gas to a patient and various different anesthetic agents are available for that purpose, both in liquid form to be vaporized for addition to a gas, as well as gaseous forms such as nitrous oxide.
One difficulty that the use of such agents has in common, however, is the need for removal of waste gases exhaled by the patient or that may otherwise enter the local environment during an over-pressure condition through exhalation valves. It is believed that such waste gases, containing the anesthetic agent, are unhealthy for continuous breathing by personnel, such as doctors, nurses, etc., that of necessity must work for long periods of time in that environment.
Thus, there have been numerous means and devices used to scavenge or prevent those waste gases from entering the local environment. One means readily available for such removal is the normal central vacuum system available in hospitals, which operate at a vacuum level of about -15 to -19 inches of mercury vacuum.
Typically, the waste anesthetic gases are discharged into the local environment through a biased valve such as a pop-off valve, or through exhaust ports found in typical demand valves. In the use of such demand valves the patient's attempt to inhale draws a slight vacuum that opens a main valve through which the anesthetic gas passes to the patient and the patient exhales through a check valve mechanism in the demand valve; the waste exhalation gases, thus passing directly to the environment through the exhaust ports. Normally, such demand valves provide a mixture of oxygen and nitrous oxide to the patient.
The solutions heretofore proposed and used have, in some manner, captured those waste gases immediately upon their passing through some type of exhaust valve and then channeling the same to the hospital vacuum system. Problems arise in interfacing between the check valve or exhaust valve that basically sees and operates by the pressures associated with the patient circuit and the vacuum systems in the hospitals. Although there must be fluid communication there-between, the vacuum system, if allowed to act upon such exhaust valves can prevent the normal valve operation. Also, there is need for means to allow the reservoir to account for the difference in flows between the patient's exhalation which is cyclical and the steady flow to the vacuum system.
Obviously, directly connecting the vacuum system to the check or exhaust valve would supply sufficient vacuum to open that valve continuously, thus the interface is needed to prevent the line vacuum from affecting the normal valve operation. Also, as to flow, the patient delivers an intermittent flow of gases during exhalation while, during inhalation, there is no flow from the patient. The exhalation flow for a normal resting patient may be in the order of 8-12 liters/minute. The vacuum supply, on the other hand is a constant draw and thus, a reservoir is used to contain the higher flows of exhaled gases until the vacuum system can catch up and remove those gases.
Presently, interfacing reservoirs are of a closed system where the reservoir is a closed container and has positive and negative valves. A positive check valve operates at normally about 10 cm H.sub.2 O and allows a path for the patient to exhale in the event the vacuum line is occluded or the vacuum system discontinued. A negative check valve is also present and is normally set to about 1/2 cm H.sub.2 O and prevents full vacuum from ever reaching the patient.
By the use of these valves in the closed system, the patient is protected. The valves, themselves, however, add a further source of trouble. At the extremely low pressure and vacuum points, such valves are quite difficult to calibrate and, of course, the valves are always subject to malfunction due to sticking.
Open systems can also be used to interface between the exhaust valve and the vacuum supply where the reservoir itself is completely open to the surrounding ambient, however, some resistance between the reservoir and that ambient is desirable to prevent all of the waste gases from entering the ambient atmosphere.